Hydraulic machines such as dozers, loaders, excavators, backhoes, motor graders, and other types of heavy equipment use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump of the machine that provides pressurized fluid to chambers within the actuators. As the pressurized fluid moves into or through the chambers, the pressure of the fluid acts on hydraulic surfaces of the chambers to affect movement of the actuators and a connected work tool. When the pressurized fluid is drained from the chambers it is returned to a low pressure sump of the machine.
One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the fluid draining from the actuator chambers to the sump often has a pressure greater than a pressure of the fluid already within the sump, especially when the actuators are moving in a direction aligned with the pull of gravity (i.e., when actuator movement is being assisted by a weight of the tool and associated load). As a result, the higher pressure fluid draining into the sump still contains some energy that is wasted upon entering the low pressure sump. This wasted energy reduces the efficiency of the hydraulic system.
One attempt to improve the efficiency of a hydraulic machine is disclosed in JP Patent Application 2010-084888 of Morihiko et al. that published on Apr. 15, 2010 (“the '888 publication”). In particular, the '888 publication discloses a hydraulic system for a machine having a boom cylinder and a swing motor connected to an accumulator. The swing motor is configured to selectively direct fluid into the accumulator during deceleration, and a head-end of the boom cylinder is configured to selectively receive fluid from the accumulator when extending in an overrunning condition. When the boom cylinder receives fluid from the accumulator, the fluid first passes through a motor connected to an engine of the machine and transfers energy to the engine via the motor.
Although the system of the '888 publication may help to improve efficiencies in some situations through storage and reuse of pressurized fluid, it may still be less than optimal. In particular, the '888 publication describes accumulating pressurized fluid from only the swing motor and discharging fluid to only a single chamber of the boom actuator. Thus, efficiency benefits obtained from the disclosed energy capture and reuse may be limited. Further, the system of the '888 publication may provide little flexibility on the direction and use of fluid exiting the boom actuator. This lack of flexibility may reduce functionality and/or efficiency of the machine.
The disclosed energy recovery system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.